Zinc is an important element in most cells, and variation from normal concentration is associated with many diseases, such as Alzheimer's syndrome (Cualungee et al., 1999; Suh et al., 2000; Xuang et al., 2000; Andrasi et al., 2000). Rapid analysis of trace metal cations requires both high sensitivity and selectivity. Fluorescent chemosensors, which consist of a recognition moiety and a signaling moiety, are particularly attractive because they are inherently highly sensitive.
One problem with the sensitivity of fluorescent chemosensors is that other metal ions may interfere. Many reported fluorescent chemosensors for Zn(II) suffer from interference from binding Cu(II), which commonly forms more stable complexes that Zn(II) with many ligands (Walkup et al., 1997; Hirano et al., 2000; Fahrnti et al., 1999).
In a previous study (Castagnetto et al., 1998), it was found the recognition of Zn(II) by compound I, shown in FIG. 1, benefited from both fluorescence enhancement as well as chiroptical signal increase. However, Cu(II) was a significant competitor for Zn(II) in that system, as it has been found to be in many published systems.
In the pharmaceutical industry, asymmetric synthesis is crucial. Chiral coordination complexes are frequently used in asymmetric synthesis and chiral discrimination technologies. Among known chiral ligands, C2-symmetric compounds have been widely and successfully used in enantioselective reactions. It has been suggested that a higher symmetry would give better control of enantioselectivity. While numerous classes of achiral C3-symmetric ligands exist, there are relatively few examples of chiral C3-symmetric ligands.